European corn borer, Ostrinia nubilalis
Male moths are visibly darker and slightly smaller than the pale yellow female moths. Adults have an average wingspan of about 25 mm (1 inch). The forewings of both genders have dark wavy lines. Eggs of European corn borer are scaly and glossy white in appearance and are laid in masses of 15 to 30 eggs. Upon hatching, larvae are cream colored or pink with small brown spots and a dark or reddish-brown head capsule. When larvae are fully developed, they are about 25 mm (1 inch) in length.
- The European corn borer is an invasive species of moth found throughout corn growing regions east of the Rocky Mountains.
- Hemp plants located near corn fields are at higher risk of European corn borer infestation.
- European corn borer can attack a wide variety of hosts including hemp, corn, pepper, snap bean, cotton, and chrysanthemums, among others.
Larva of European corn borer on a corn leaf. The European corn borer is a species of moth that can attack hemp in addition to a wide variety of agricultural and ornamental plants. Hemp plants located near corn fields are at a high risk of infestation. There are very few insecticides registered for use in hemp since its cultivation has only recently been legalized in the United States. Image credit: Adam Sisson, Iowa State University, Bugwood.org
Mass of European corn borer eggs on corn leaf. Image credit: Frank Peairs, Colorado State University, Bugwood.org
Recently hatched European corn borer. Image credit: Phil Sloderbeck, Kansas State University, Bugwood.org
European corn borer pupating on a corn leaf. Image credit: Frank Peairs, Colorado State University, Bugwood.org
Adults of European corn borer. Image credit: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Life history and habits
Larvae overwinter in stalks of corn and other host plants. They pupate in early spring and moths emerge in late May or early June. Female moths search for suitable host plants such as hemp to lay eggs. After hatching, larvae develop over four to six weeks and begin to pupate. European corn borers typically have two generations per growing season in Colorado.
After hatching from eggs, larvae of European corn borer enter the hemp stalk and feed within the plant. This feeding injury results in reduced yields and weakens the stalks, making plants more prone to breakage. Other signs of feeding injury include stem wounds, holes in stems, discoloration of plant tissue, and sometimes the presence of frass (feces) that resembles sawdust. Crops near corn fields are more susceptible to infestation.
To monitor moth flights, Heliothis traps baited with a pheromone lure can be deployed a minimum of 50 feet apart along the field edge. The bottom of the trap should be positioned no more than 4 inches above grassy weeds and should not be placed above bare ground. Check traps once or twice each week and replace the lures every two weeks.
Regular scouting of crops for eggs should begin in early spring and is an easy way to monitor pest densities. To do this, inspect the top and bottom of leaves and along plant stems. Be sure to choose plants randomly when scouting for a more accurate representation of the entire field. In other crops such as corn, treatments are recommended when plants display symptoms of feeding injury, or when 15% or more of plants are colonized by European corn borer. Repeated applications are recommended if caterpillars are present on 15% or more of hemp plants sampled 4-7 days after the first treatment.
Removing crop residues after harvest, autumn plowing, and spring tillage are recommended. Planting trap crops, such as corn, adjacent to cultivated fields will draw egg-laying moths away from hemp plants. Hemp seedlings can also be transplanted early before pests begin to migrate into the fields.
There are several natural enemies of European corn borer, including green lacewings, ladybugs, and Trichogramma wasps. Plant flowering plants near the hemp field to encourage the presence of natural enemies. The Trichogramma wasps attack eggs of European corn borer and prevent them from hatching. The wasps are commercially available as biological control agents for European corn borer and should be released when moths begin laying eggs.
Insecticide applications are effective when they target newly hatched caterpillars before they bore into the stem, which highlights the importance of scouting crops for eggs early in the season. There are very few insecticides registered with the EPA for use in hemp since its production was recently legalized in the United States. Consult the National Pesticide Information Retrieval System for more information on pesticide registration by state.
Canadian Hemp Trade Alliance. 2022. Insects and Pests. Available https://www.hemptrade.ca/content.aspx?page_id=22&club_id=950211&module_id=409588
Texas Department of Agriculture. (n.d.). European Corn Borer. Available https://www.texasagriculture.gov/Regulatory-Programs/Plant-Quality/Pest-and-Disease-Alerts/European-Corn-Borer
University of Vermont. 2020. The European Corn Borer in Hops and Hemp. University of Vermont. Available https://blog.uvm.edu/outcropn/2020/07/02/the-european-corn-borer-in-hops-and-hemp/#:~:text=As%20the%20production%20of%20hemp,damaging%20to%20hundreds%20of%20plants
University of Vermont. (n.d.). The European Corn Borer in Hops and Hemp. University of Vermont: Extension. Available https://www.uvm.edu/sites/default/files/Northwest-Crops-and-Soils-Program/Articles_and_Factsheets/European_Corn_Borer_Hemp_Hops_factsheet_FINAL.pdf